Aggregatibacter actinomycetemcomitans QseBC is activated by catecholamines and iron and regulates genes encoding proteins associated with anaerobic respiration and metabolism

Aggregatibacter actinomycetemcomitans QseBC regulates its own expression and is essential for biofilm growth and virulence. However, the signal that activates the QseC sensor has not been identified and the qseBC regulon has not been defined. In this study, we show that QseC is activated by catecholamine hormones and iron but not by either component alone. Activation of QseC requires an EYRDD motif in the periplasmic domain of the sensor and site-specific mutations in EYRDD or the deletion of the periplasmic domain inhibits catecholamine/iron-dependent induction of the ygiW-qseBC operon. Catecholamine/iron-dependent induction of transcription also requires interaction of the QseB response regulator with its binding site in the ygiW-qseBC promoter. Whole genome microarrays were used to compare gene expression profiles of A. actinomycetemcomitans grown in a chemically defined medium with and without catecholamine and iron supplementation. Approximately 11.5% of the A. actinomycetemcomitans genome was differentially expressed by at least two-fold upon exposure to catecholamines and iron. The expression of ferritin was strongly induced, suggesting that intracellular iron storage capacity is increased upon QseBC activation. Consistent with this, genes encoding iron binding and transport proteins were down-regulated by QseBC. Strikingly, 57% of the QseBC up-regulated genes (56/99) encode proteins associated with anaerobic metabolism and respiration. Most of these up-regulated genes were recently reported to be induced during in vivo growth of A. actinomycetemcomitans. These results suggest that detection of catecholamines and iron by QseBC may alter the cellular metabolism of A. actinomycetemcomitans for increased fitness and growth in an anaerobic host environment.

Integration host factor is required for replication of pYGK-derived plasmids in Aggregatibacter actinomycetemcomitans

In this study, we show that integration host factor protein (IHF) is required for replication of pYGK plasmids in Aggregatibacter actinomycetemcomitans. YGK plasmids were not replicated in A. actinomycetemcomitans strains lacking either the α- or β- subunit of IHF. However, the deletion mutants were complemented, and plasmid replication was restored when the promoter region and gene for either ihfA or ihfB was cloned into pYGK. We also identified two motifs that resemble the consensus IHF-binding site in a 813-bp fragment containing the pYGK origin of replication. Using electrophoretic mobility shift assays, purified IHFα-IHFβ protein complex was shown to bind to probes containing either of these motifs. To our knowledge, this is the first report showing that plasmid replication is IHF-dependent in the family Pasteurellaceae. In addition, using site-direct mutagenesis, the XbaI and KpnI restriction sites in the suicide vector pJT1 were modified to generate plasmid pJT10. The introduction of these new unique sites in pJT10 facilitates the transfer of transcriptional or translational lacZ fusion constructs for the generation of single-copy chromosomal insertion of the reporter construct. Plasmid pJT10 and its derivatives will be useful for genetic studies in Aggregatibacter (Actinobacillus) and probably other genera of Pasteurellaceae, including Haemophilus, Pasteurella, and Mannheimia.